For example, when the energization of an inductive load such as a solenoid of a hydraulic pump is controlled, a PWM drive control may be performed. In that case, a control unit generates a PWM pulse, and controls the energization of the inductive load according to the PWM pulse. However, when the control is performed at a fixed frequency, there may arise such a problem that an audible sound may occur during the control according to a structure of the actuator.
To cope with the problem on the sound described in the description of the related art, it has been confirmed that quietness can be improved by frequency spreading of a PWM pulse. However, when the frequency of the PWM pulse is spread to feedback control the inductive load such as the solenoid, as schematically illustrated in FIG. 12, a control current may overshoot or undershoot, for example, at the moment of switching the frequency (refer to portions RT1 and RT2 in FIG. 12). Therefore, it is required to stabilize a mean current of the control current even if the frequency of the PWM pulse is spread. In order to stabilize the mean current, a method of setting the frequency to an intermediate frequency as disclosed in Patent Literature 1 can be used. However, because a long period of time is required to stabilize the current, which is not desired.
An example of related art includes JP-A-2010-061481 (Patent Literature 1)